Electrophysiological Effects of the Drosophila Neuropeptides PDF and sNPF

VECSEY, C.G. ; PÍREZ, N.; GRIFFITH, L.C.

Cold Spring Harbor, New York, Estados Unidos

Conferencia; Neurobiology of Drosophila Meeting; 2011

Cold Spring Harbor Laboratory

Neuropeptides have potent and diverse effects on behavior in Drosophila melanogaster, but how these neuropeptides alter the activity of their target cells is poorly understood. Oocyte recordings have the significant drawback that the recordings are not being done in the species or cell type of interest, whereas recording from cells natively expressing the receptor is often unfeasible. Therefore, in this study we utilized patch-clamp recordings of third instar larval motor neurons to assess the electrophysiological effects of two neuropeptides, pigment-dispersing factor (PDF) and small neuropeptide F (sNPF), which play important roles in sleep/rhythms and feeding/metabolism, respectively. To do this, an OK371-Gal4 driver was used to express the only known receptor for each neuropeptide (PDFR or sNPFR1) in motor neurons. Treatment with PDF caused a depolarization of approximately 8 mV in motor neurons over-expressing PDFR, which resulted in increased firing in response to a range of current injections. PDF had no significant effect in control animals that did not over-express PDFR in motor neurons, suggesting that larval motor neurons do not natively respond to PDF. sNPF treatment had the opposite effect, producing a dose-dependent hyperpolarization of motor neurons that were caused to express sNPFR1, and a corresponding reduction in firing in response to current injections. Co-expression of sensors for either calcium (GCaMP3) or cAMP (Epac-cAMPs1) allowed us to determine if these intracellular signaling molecules are affected by sNPF. We found that sNPF caused a small but significant decrease in cAMP levels in motor neurons over-expressing sNPFR1. We also observed that when the ventral forebrain was experiencing repeated spontaneous calcium waves, sNPF treatment caused these waves to cease. Our findings with PDF corroborate and expand upon previous reports that PDF is positively coupled to cAMP production, which is typically stimulatory. In contrast, our studies show for the first time in Drosophila neurons that sNPF is inhibitory and negatively coupled to cAMP levels. Future studies will attempt to determine which channels mediate the electrophysiological effects of PDF and sNPF, and if these neuropeptides alter the responses to other neurotransmitters. Finally, it will be of interest to know if these neuropeptides also have similar effects in adult CNS cells in which their respective receptors are natively expressed. Knowledge of how these neuropeptides affect their target cells at the electrical and molecular level will help interpret the findings of behavioral studies in which their function is manipulated genetically or pharmacologically.